Owner's Problem Description
The owner reports that the 2002 Oldsmobile Bravada starts fine with fuel pressure at 52 PSI but loses pressure to zero after shutdown and won't restart until it sits for a while. There are intermittent stalls, and the owner recently replaced both the neutral safety switch and ignition switch, unsure if related. The air ride compressor has also stopped working. Assistance is requested.
Professional Technical Analysis
The 2002 Oldsmobile Bravada is equipped with a 4.2L inline 6 engine, and with approximately 120,000 miles on the odometer, the vehicle exhibits fuel delivery issues primarily characterized by an inability to maintain fuel pressure after the engine is turned off. The fuel pressure initially measures 52 PSI but drops to zero immediately after shutdown, preventing restart. This issue may stem from several factors: a failing fuel pump, a faulty fuel pump relay, or a defective oil pressure switch. The fuel pump operates under the control of a relay and receives power from the oil pressure switch; if the relay fails or if there are wiring issues, the pump may not activate correctly. Since the owner has already experienced starting problems related to the neutral safety and ignition switches, there is a possibility of wiring or grounding issues contributing to the fuel delivery failure. Given the vehicle's symptoms, a thorough examination of the fuel pump circuit, including power supply during cranking and the integrity of the relay, is essential. The air ride compressor issue may be unrelated but should be considered as a potential electrical system drain affecting fuel pump operation. Current assessments indicate immediate safety concerns as the vehicle may stall unexpectedly, compromising the driver's control. Electrical connections should be inspected for corrosion or wear, particularly at the pump connector, which is known to develop issues due to heat and moisture exposure. Proper diagnostics using the GeekOBD APP to monitor fuel pressure in real-time and check for fault codes related to the fuel system and electrical components will be valuable in pinpointing the root cause.
Possible Causes
Most common causes (ordered by frequency):
- Fuel Pump Failure: The fuel pump may be experiencing intermittent failure, failing to maintain pressure after the engine is shut off. When the ignition is turned on, the pump should prime and hold pressure, but if it fails, it will drop to zero. The pump should be tested for proper operation and output pressure should be verified with a gauge, ideally maintaining 60-66 PSI under load during operation. If the pump is not supplying adequate pressure, it may need to be replaced (OEM Part # 19117080, cost approximately $200-400). - Fuel pressure gauge readings dropping to zero after engine shutdown, verified operation during testing when power is directly applied, inconsistent fuel delivery observed during cranking.
- Fuel Pump Relay Malfunction: The relay supplying power to the fuel pump may be faulty or intermittently failing. The fuel pump relay should be tested for continuity and proper operation, ensuring it engages when the ignition is turned on. A good relay should have continuity on both the control and load sides, and should operate within specifications. If the relay is not functioning, it may require replacement (OEM Part # 12115525, cost approximately $20-50). - No power at the pump connector during cranking, relay clicks but does not supply voltage, documented evidence of relay failure in similar models.
- Oil Pressure Switch Failure: The oil pressure switch acts as a secondary switch for the fuel pump, and if it fails, it may not provide power to the pump, especially when the engine is off. Testing the switch for continuity and proper operation when the engine is running versus off is crucial. A faulty switch can prevent the pump from receiving power, requiring replacement (OEM Part # 25317982, cost approximately $30-60). - Intermittent power loss to the pump when the ignition is on but the engine is off, confirmed with continuity tests showing failure in the switch, related fault codes may be present.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial Fuel Pressure Test: Begin by confirming the fuel pressure with a gauge at the fuel rail. The pressure should be maintained at 60-66 PSI while the engine is running. If the pressure drops to zero after shutdown, this points towards either a leaking fuel injector or a failing fuel pump. This test will provide initial insight into the fuel delivery system's integrity.
- STEP 2 - Power Supply Check: With the ignition in the 'on' position but the engine off, use a multimeter to check for voltage at the fuel pump connector. You should see 12V at the connector indicating the pump relay and oil pressure switch are functioning. If there is no voltage, further investigation into the relay and switch is necessary.
- STEP 3 - Relay and Oil Pressure Switch Testing: Test the fuel pump relay for continuity and operation. Ensure that it engages when the ignition is turned on. Also, check the oil pressure switch for proper operation since it can affect fuel pump activation. Replace any components that do not meet specifications or show signs of failure.
- STEP 4 - Wiring and Connector Inspection: Inspect the wiring harness and connectors leading to the fuel pump for signs of wear, corrosion, or damage. Clean and repair any poor connections. Ensure that the ground connections are solid and that there are no breaks in the wiring that can interrupt power to the pump.
